This invention relates to an automatic photodrawing machine and, more particularly, to a projecting optical system which can be mounted on the movable carrier of an automatic photodrawing machine so that, when said movable carrier and drawing plates are stationary, it is operative to photocopy apertures having any desired configurations such as dots, letters, numerals, signs and symbols onto a light sensitive material and, when said movable carrier moves relative to the surfce of said light sensitive material, to draw desired lines on said light sensitive material.
Generally, the thickness of one type of light sensitive material, such as those made in the form of a dry plate, differs from the thickness of other types such as those made in the form of film. Moreover, even as to different samples of light sensitive materials of the same type, there are sample-to-sample variations in thickness. In use of these light sensitive materials it has heretofore been necessary to pay special attention to such variations in thickness.
Nevertheless, most conventional photodrawing machines do not provide any compensation for the displacement of the focal plane caused by the variation in thickness of the light sensitive material being used; instead, drawing operations are carried out under out-of-focus conditions. Even in several conventional photodrawing machines having a focus readjusting capability, the compensation of displacement of the focal plane is effected only by adjusting the projecting lens rather than by displacing the aperture to be projected and the drawing plate. Accordingly, an error is caused in the projecting magnification and hence in the width of lines being drawn. The variation in the projecting magnification also leads to the variation in illumination of the projected point and hence to an undesirable variation in the width of lines being drawn.
As to exposure control, it is conventional in connection with diahragm mechanism to vary opening area thereof in a preselected plane either by operating a diaphragm plate or by screening the light flux with a material having a variable light transmission factor to effect the exposure control. In a photodrawing machine, however, it is not practical to vary the opening area by operting a diahragm plate because no mechanically durable mechanism has heretofore been provided for this purpose. As to the method of screening the light flux with a material having a variable light transmission factor, this could be done in several ways. For example, an optical filter such as optical wedge could be used. As another example, a combination of a polarizing plate and a liquid crystal or crystal such as KDP could be used. However, where an optical filter is used, a difficulty is encountered in maintaining the light transmission at a constant level. On the other hand, the use of a crystal such as KDP involves a difficulty in controlling the incident angle of the light flux, and the use of a liquid crystal involves a difficulty in regard to the response and contact ratio. Thus, all of these conventional methods involves different difficulties and are not very advantageous for use in a high-speed light quantity controlling diaphragm device.